Pulse-echo ranging systems, also known as time-of-flight ranging systems, are often used in level sensing and level measurement applications. Pulse-echo ranging systems determine the distance to a reflective surface (i.e. reflector) by measuring the length of time following a transmission of a burst of energy pulses that the echo or reflected pulse is received. Ultrasonic pulses or microwave signals are typically used in pulse-echo systems.
Pulse-echo ranging systems typically include a transducer and a microprocessor or signal processor operating under stored program control. The transducer both sends and receives pulses. The system typically includes an energy reservoir (for example, for loop powered applications) which is coupled to the transducer. The energy reservoir stores the leftover energy that is not consumed by the other power-consuming components in the circuit.
The amount of transmit energy output by the transducer is dependant upon the energy stored in the energy reservoir. The microprocessor typically includes a code component (i.e. function or routine) that monitors the reservoir voltage and only allows the transducer to transmit when the reservoir voltage is above a threshold voltage level.
It will be appreciated that a fixed threshold voltage imposes a trade-off between speed and accuracy. The threshold voltage has an effect on the accuracy of the measurement. A greater threshold voltage results in a greater ultrasonic output signal, which in turn generates an improved echo with greater echo strength and confidence.
A higher threshold voltage also requires more time for the energy reservoir to reach the threshold value, resulting in a greater elapsed time between consecutive measurements.
One approach encompasses storing a constant threshold voltage value in memory. The constant value allows the unit to meet measurement accuracy and update timing specifications but it does not provide for flexibility to optimize measurement reliability or update time beyond the specification.
In view of the foregoing, there remains a need for improved method and apparatus to address the shortcomings in the art.